JPH0696478B2 - Single crystal automatic growth method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a single crystal growth method, and more specifically, a floating zone method (hereinafter,
"FZ method") for the automatic growth of single crystals.

(Prior Art) The FZ method by high-frequency induction heating is an optimal method for growing a single crystal of a high melting point substance because a sample itself becomes a heating element without using a crucible.

Currently, a LaB ₆ (melting point 2600 ° C) single crystal, which is a thermionic emission material, is grown by this method and is widely put to practical use.
In addition, TiC (melting point 3
(100 ° C) single crystal is also grown by this method. Recently, along with the demand for materials that can withstand the harsh conditions of use, the growing method of single crystals by the high frequency heating FZ method is becoming more and more important.

(Problems to be Solved by the Invention) By the way, when a single crystal is grown by the high frequency heating FZ method, the shape of the zone changes as the zone is heated. It is difficult to obtain crystals.

However, in the conventional single crystal growth method by the FZ method, there is no device that can detect the growth state of the crystal well, such as the load cell in the single crystal growth by the pulling method, so the experimenter directly observes the zone shape. However, the heating power had to be manually controlled so as to have an appropriate value to grow a single crystal. Therefore, it is difficult to control the temperature gently by manually controlling the temperature, which deteriorates the quality of the single crystal. Moreover, the quality of the grown crystal also varies.

The present invention eliminates the above-mentioned drawbacks of the prior art, and when growing a single crystal by the FZ method by high frequency induction heating, an object thereof is to provide a method capable of automatically growing the single crystal while smoothly controlling the temperature. is there.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies to achieve the above object, and it is important to keep the shape of the melt zone constant for smooth single crystal growth. It has been found that the change in the shape of the zone is caused by the deviation from the appropriate heating power and can be determined by the correlation between the high frequency current heating the zone and the anode voltage. As a result, it became possible to grow the single crystal completely automatically by reading the high frequency current and the anodic voltage during the growth of the single crystal, judging the zone shape by the computer, and controlling the heating power.

Alternatively, the change in the zone shape can also be determined by the change in the high-frequency current heating the zone, and therefore, the change in the zone shape is determined by the computer from the change in the high-frequency current during single crystal growth, and heating is performed. By controlling the power,
It has become possible to grow single crystals completely automatically.

Based on the above knowledge, the invention of the single crystal automatic growth method by the FZ method has been completed.

That is, the single crystal automatic growth method according to the present invention, in the method of growing a single crystal by the FZ method utilizing high frequency induction heating, by comparing the anode voltage of the high frequency oscillator tube and the high frequency current, the zone shape Judgment, controlling heating power based on the judgment result, or judging the change of the zone shape from the change of high-frequency current during growth, and controlling the heating power based on the judgment result. Then, the heating power is controlled.

The present invention will be described in more detail below.

(Operation) FIG. 1 is a conceptual diagram of an example of the FZ method automatic single crystal growing furnace used in the method of the present invention.

In the figure, 1 is an upper shaft, 1'is a lower shaft, 2 and 2'is a holder, 3
Is a sintered rod, 3'is a melt zone, 4 is a grown single crystal, 5 is a high frequency work coil, 6 and 7 are anode voltage measuring instruments for high frequency current, 8 is a computer, 9 is a high frequency oscillator (oscillation tube). ), 10 is a calculation unit, and 11 is a control unit.

In such a structure, first, a raw material sintering rod 3 for growing a single crystal is set on the upper shaft 1 via a holder 2, and a single crystal or a sintering rod is placed below the holder 2'as an initial zone forming material. Fixedly supported via. Next, after filling the growth furnace with an inert gas such as Ar or He at a few atmospheres, the end of the initial zone forming material is melted by induction heating from the high frequency coil 5 to form a zone 3 ', and the upper shaft 1 Then, the lower shaft 1'is slowly moved downward (0.2 to 5 cm / hr) to start growing a single crystal.
Up to this point, it is the same as the conventional growing method.

After starting the movement of the melt zone, the zone is moved about 5 mm and the single crystal is automatically grown by the method of the present invention. However, the shape of the ligament when growing is the first
The shape shown in 3'of the figure is ideal, and the shape depends on the moving speed ratio between the sintered rod 3 and the crystal 4 being grown. Therefore, if the zone is moved by about 5 mm, a regular zone shape is obtained, and hence the method of the present invention is applied thereafter.

By a preliminary experiment, the relationship between the high-frequency current and the anode voltage of the oscillation tube when the shape of the object to be heated (melting zone) did not change was obtained in advance. As a result, it was found that the two have a nearly proportional relationship (A / Vα = constant). Therefore, if the ratio of the two zones is taken during the growth of the single crystal, the computer determines whether the zone shape is appropriate, and the heating power is controlled, the zone shape can always be maintained properly.

If the heating power is higher than the appropriate value during the growth of the single crystal, the length of the melt zone becomes wide and the density of the sintered rod 3 is not 100%. The impedance of becomes small, and a large amount of high-frequency current flows out. On the other hand, conversely, if the heating power is lower than the proper value, the reverse change appears. Therefore, the high frequency current and the anode voltage detected by the measuring instruments 6 and 7 are calculated by the arithmetic unit 10 to obtain a ratio of the two,
Based on the ratio, the zone shape is compared with the set value to determine suitability, and the control unit 11 of the computer 8 controls the heating power.

The above is the first zone control method according to the present invention.

Further, when the melt zone 3'is thin during the growth of the single crystal, the impedance between the coil 5 and the melt zone becomes small, and a large amount of high-frequency current flows out. On the other hand, conversely, if the melt zone 3'is thicker, the high frequency current becomes smaller. Therefore, the high frequency current is measured by the measuring device 6.
Alternatively, the calculation unit 10 may determine the change in the zone shape from the change, and the control unit 11 of the computer 8 may control the heating power.

When actually growing a single crystal, how much high-frequency current changes and how much heating power should be controlled appropriately depend on the material of the single crystal. Based on the results of preliminary experiments for crystal growth, it is decided for each single crystal material and reflected in the program.

The above is the second zone control method according to the present invention.

Furthermore, if the first zone shape control method and the second zone shape control method are used together, an appropriate zone shape can be more effectively maintained.

In any of the methods, it is important to smoothly melt the sintered rod 3 into the melt zone 3'for stable automatic growth. If this is not smooth, the shape of the melt zone will change. The high-frequency current changes, and smooth heating power control becomes impossible. Therefore, it is important to make a sintered rod having a straight and uniform thickness.

As described above, the computer 8 has the power control capability for the proper heating power, but additionally has the output stabilization capability for holding the anode voltage at the set anode voltage. That is, it depends on the output stabilization method in which the measuring device 7 detects the anode voltage, compares it with a set value, and feedback-controls the result to the high-frequency oscillator (oscillation tube) 9. in this case,
The measuring device 7 is preferably a digital type. Furthermore,
If the filament voltage is made constant by using a constant voltage power source as the filament power source 12 of the high frequency oscillator (oscillation tube) 9,
More effective.

According to the method of the present invention, the shape of the melted zone is kept constant, so that there is an advantage that the diameter of the grown crystal becomes uniform.

(Example) Next, an example of the present invention will be described.

Example 1 This example is an example of growing a V ₈ C ₇ single crystal.

Preliminary experiments confirmed that it is preferable to control the zone composition to C / V = 0.97 and the composition of the raw material sintered rod to C / V = 0.877 for growing V ₈ C ₇ single crystal.

First, a small amount of camphor as a binder was added to vanadium carbide powder and mixed, followed by cold embossing to produce 1 × 1 × 20 cm ³
The prism was molded. This was bar-pressed at 1000 atm, then formed into a cylindrical shape, and a sintered rod was produced at 2000 ° C. in vacuum.

Then, this sintered rod was fixed to the upper shaft of the FZ growth furnace via a holder, and the vanadium carbide single crystal <100> was fixed to the lower shaft, and a carbon disk (about 0.05 g) was sandwiched between them. . After filling the growth furnace with 7 atm of He, the surroundings of the graphite disk are melted by high frequency heating to form the initial melt zone, the sintered rod is melted into the melt zone at 1 cm / hr, and the single crystal is grown at 0.75 cm / hr. Started.

After moving the zone of about 0.05 cm, the present invention was applied to carry out automatic growth. Growth heating conditions are: anode voltage 5KV, high frequency current 1
90A. Regarding the heating power control condition, when the ratio of high frequency current to anode voltage (A / V) changed by 0.1%, the anode voltage was changed by several volts and single crystals were grown automatically.

The obtained vanadium carbide single crystal has a uniform diameter (0.85c
m) and the length was 6.5 cm. As a result of analysis, the carbon contents at the beginning, the center, and the end were 17.13 wt% and 17.12, respectively.
wt% and 17.08Wt%, and C / V = 0.
It was 877, 0.876 and 0.874. The vanadium carbide single crystal is known as a crystal that easily cracks, but the single crystal grown by the method of the present invention had no cracks at all. This is considered to be because the single crystal was grown by the present invention with a uniform thickness and without a sudden temperature change.

Example 2 This example is an example of growing a TiC _0.96 single crystal.

To grow this titanium carbide single crystal, the zone composition is C / Ti = 1.
3. It was confirmed by preliminary experiments that the composition of the raw material sintered rod should be controlled to C / Ti = 0.99.

First, a small amount of camphor as a binder was added to and mixed with titanium carbide powder, and then cold stamped to form a 1 × 1 × 20 cm ³ prism. After rubber pressing this to 1000 bar,
It was molded into a cylindrical shape, and a sintered rod was produced at 2000 ° C. in vacuum.

Then, this sintered rod was fixed to the upper shaft of the FZ growth furnace via a holder, the titanium carbide single crystal <100> was fixed to the lower shaft, and a carbon disk (about 0.05 g) was sandwiched between them. . After filling the growth furnace with He at 7 atm, the vicinity of the graphite disk was melted by high frequency heating to form the initial melt zone, and the sintered rod was melted into the melt zone at 1.2 cm / hr, and the single crystal at 1.0 cm / hr. The cultivation has started.

After moving the zone of about 0.5 cm, the method of the present invention was applied to start automatic growth. At that time, the growth heating condition was an anode voltage of 6.06.
It was 9KV and high frequency current 216.1A. In the case of TiC single crystal growth, if the heating power is higher than the appropriate value, the length of the melt zone becomes wide and the density of the sintered rod is not 100%, so the melt zone becomes thin and the gap between the work coil and the melt zone Impedance becomes small and a lot of high frequency current starts to flow. On the other hand, conversely, if the heating power is lower than the proper value, the reverse change appears. Therefore, as the control condition of the heating power during the automatic growth, when the high frequency current changed by 0.2 A, the anode voltage was changed by 9 V so as to cancel this change.

The following controls were also used together.

That is, from the ratio of the high frequency current and the anode voltage
It was detected every minute, and when the ratio value changed by 0.02 or more from the ratio value (= 216.1 / 6.069) at the time of starting the automatic growth, the anode voltage was changed by 5V. That is, when the ratio value increased by 0.02 or more (when the melt zone became thin), the anode voltage was lowered by 5V. In the opposite case, the anode voltage was increased by 5V.

By performing such heating power control, stable zone transfer for 5 hours and 30 minutes was performed automatically, and the obtained TiC _0.96
The single crystal had a uniform diameter (0.9 cm) and a length of 6 cm. The quality of the single crystal was smaller than that of the manual growth, and a good quality was obtained. This is considered to be because the single crystal was grown by the present invention with a uniform thickness and without a sudden temperature change.

Example 3 This example is an example of growing a LaB ₆ single crystal.

LaB ₆ powder was sintered in the same manner as in Example 2 to prepare a sintered rod having a diameter of about 1 cm and a length of 20 cm. This was fixed to the upper and lower shafts of the FZ growth furnace via a BN holder. After filling the growing furnace with He at 8 atm, the initial zone was formed by high frequency heating. The zone transfer was performed by moving the sintered rod and the grown single crystal downward at a speed of 1 cm / hr.

After moving the zone of about 0.5 cm, the method of the present invention was applied to start automatic growth. At that time, the heating conditions for the growth are anode voltage 5.
It was 609KV and high frequency current 200.7A.

In the case of growing a LaB ₆ single crystal, the melt zone was more likely to drop than in the case of TiC of Example 2, and it was necessary to adjust the heating power with a small change in the high frequency current. That is, the high frequency current
When 0.1A was increased, the anode voltage was lowered by 4V. In addition, when the high frequency current decreased by 0.1 A (when the zone became thicker), the zone tended to fall, so the anode voltage was similarly lowered by 3.5V. for that reason,
The heating power decreased as the zone moved. This is because the melting zone composition changed due to evaporation, so that the melting point of the zone decreased as the zone moved. The heating conditions at the end of the automatic growth for 5 hours were 5.474V and 195.2A.

In this way, a LaB ₆ single crystal having a diameter of 8 mm and a length of 5.5 cm was obtained. With a manually grown single crystal, the surface is not smooth because the melting zone falls and grows slightly, but with the automatically grown single crystal, fine heating power control is performed, so the surface is very smooth. is there. The quality of the second embodiment
Similar to TiC, the variation was small and the quality was good.

(Effect of the invention) As described above, according to the present invention, when growing a single crystal by the FZ method by high frequency induction heating, by comparing the anode voltage of the high frequency oscillator tube and the high frequency current, Judgment or change of the zone shape from the change of high frequency current, and heating power is controlled based on the result of judgment, so single crystal can be grown automatically with smooth temperature control, and high quality single crystal is cheap Can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an example of an FZ method automatic single crystal growth furnace used in the method of the present invention. 1 ... Upper shaft, 1 '... Lower shaft, 2, 2' ... Holder, 3
...... Sintered rod, 3 '... Melting band, 4 ... Grown single crystal, 5
…… High frequency work coil, 6 …… High frequency current measuring instrument, 7
…… Anode voltage measuring instrument, 8 …… Computer, 9 …… High-frequency oscillator (oscillation tube), 10 …… Computing section, 11 …… Control section,
12 ... Oscillator filament power supply.

Claims (4)

[Claims] 1. A method for growing a single crystal by a floating zone method using high-frequency induction heating, wherein a fusion zone shape is determined by comparing an anode voltage of a high-frequency oscillation tube with a high-frequency current, and the determination result is obtained. A single crystal automatic growth method characterized by controlling heating power based on the above. 2. The comparison between the anode voltage and the high frequency current of the high frequency oscillator tube is made by the ratio of the anode voltage and the high frequency current.
The method described in. 3. A method for growing a single crystal by a floating zone method using high frequency induction heating, wherein a change in a zone shape is judged from a change in a high frequency current during the growth, and heating power is supplied based on the result of the judgment. A single crystal automatic growth method characterized by controlling. 4. The method according to claim 3, further comprising a method of determining the shape of the melted zone by comparing the anode voltage of the high frequency oscillation tube with the high frequency current and controlling the heating power based on the determination result. A single crystal automatic growth method characterized by the above.